Induction heater for drums

ABSTRACT

An induction heater (1) includes a substantially cylindrical jacket adapted to be placed around an article which is to be induction heated, an induction coil (5) arranged within the jacket, and protuberances (4) projecting inwardly from the internal surface of the jacket to keep the article spaced apart from the surface so as to avoid abrasion of the surface by the article. The protuberances (4) may be axially extending ribs, and may incorporate a device, such as an embedded layer, to provide a change in the visible color thereof when worn down. A multipart construction is given for the heater, in which the coil (5) is wound onto an inner former (2) and outer shells (6) are located over the coil.

FIELD OF INVENTION

The present invention is concerned with an apparatus for heating, moreparticularly the invention concerns the heating of drums and theircontents.

BACKGROUND OF THE INVENTION

Many industrial and chemical products have a high viscosity at lowtemperatures, and it is therefore often difficult to handle quantitiesof such products contained in drums under cold or cool conditions.Furthermore, it is common to store the above-mentioned products outsideof manufacturing plant, and although the interior of the plant may be ata temperature sufficient to lower the viscosity of the product, the rateof heat transfer into the drum or other container may be insufficient towarm the contents quickly if the product is needed urgently.

As a consequence, various means for heating drums have been suggested.

In the known prior art, drums and other such containers have been heatedby steam coils or jackets or by radiant electrical heating in order thatthe contents may be handled at a temperature at which the viscosity ofthe content is lower than the viscosity at the ambient temperature. Ithas also been suggested that induction heating could be employed as analternative to radiant and/or steam heating.

It is found that the cost of constructing a robust induction heater isprohibitive. Known induction heaters suffered from inevitablemishandling during use, which resulted in the exposure of, and damageto, the current carrying windings. This is not only dangerous to theuser, but also necessitates replacement of the heater.

SUMMARY OF INVENTION

According to one aspect of the present invention there is provided aninduction heater comprising a substantially cylindrical jacket adaptedto be placed around an article which is to be induction heated, and aninduction coil arranged within the jacket, characterized in thatprotuberances project inwardly from the internal surface of the jacketto keep the article spaced apart from the said surface so as to avoidabrasion of the surface by the article.

By providing the abovementioned inwardly projecting protruberances, itis possible to greatly reduce the abrasion of the inner surface of thearticle and so prevent exposure of the conducting coils which lie belowthe said inner surface.

Conveniently the protuberances are axially extending ribs.

Although the magnetic flux through the interior of the coil issubstantially uniform near the centre of the coil, there is somevariation from the ideal Helmholz field. In the interests of uniformheating the article is thus located by means of the axialprotruberances.

Preferably, the protuberances incorporate means to provide a change inthe visible colour thereof when worn down.

In order to prevent damage to the coils after extended use, it has beenfound useful to incorporate a coloured material into the ribs as a layerprovided towards the base of each rib. As the rib is worn down towardsthe inner surface of the jacket, the coloured material becomes exposedand provides an indication that the induction heater should be re-lined.Although it is considered that the most useful coloured material wouldbe relatively hard and therefore not mark the drum, it is alsoconsidered that in certain applications the coloured material could besufficiently soft to leave a visible mark on the drum.

Typically, the induction heater comprises a cylindrical jacket and aninduction coil, the jacket comprising a cylindrical former on theoutside of which the coil is wound, and an outer cover in the form of aplurality of part-cylindrical segments joined together to cover theoutside of the coil.

By employing this form of construction, preferably with two shellsforming the outer cover, it is possible to construct an induction heaterhaving a relatively smooth outer surface. This is important in manyapplications where hygenic conditions are required. Furthermore themulti-part construction aids rebuilding of the heater when the wearlimit is reached.

The protuberances may be integral with the cylindrical jacket, or may besecured thereto by glue or some suitable fixing means.

In a particular embodiment the invention consists of an induction heaterwhich comprises a substantially cylindrical jacket adapted to be placedaround an article which is to be heated, wherein the jacket includes aninduction coil to inductively heat the article, and a plurality of ribsdisposed upon the inner surface of the jacket to keep the article spacedapart from the surface to avoid abrasion of the surface by the article,wherein each rib is attached to the surface by an adhesive substancecontaining carbon-black.

It should be understood that it is possible to heat a drum and contentswhich are not in themselves electrically conductive, provided that atleast one conducting body is disposed within and electrically insulatedfrom the induction coil, whereby when an article is placed in contactwith the body and currents are induced within the body, inductiveheating of the body results in a transfer of heat to the article.

It is therefore possible to heat articles which are not inherentlyconductive such as polythene drums or glass containers.

Although the invention has been defined in general terms it should beunderstood that the most preferable embodiment of the invention residesin an induction heater for drums and/or their contents.

The preferred material for the construction of the heater is a fibreglass/resin composite material, which may be treated with a suitablefire retardant, if not inherently fire retardant.

DESCRIPTION OF DRAWINGS

In order that the invention may be further understood it will bedescribed by way of example and with reference to the accompanyingdrawings wherein:

FIG. 1. Shows a section (partially broken) through a drum heateraccording to the present invention.

FIG. 2. Shows a detail of the drum heater of figure one, particularlyrelating to the ribs.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT

Turning to FIG. 1 there is shown an inductive drum heater (1),comprising an inner glass-fibre composite former (2) having flanged ends(3). The inner former (2) is provided with a plurality of inwardlyprojecting ribs (4) which serve to locate an article within the heaterand protect the inner surface of the former (2) from abrasion anddamage. The flanged ends (3) are provided with apertures (12) to be usedas lifting holes.

A continuous coil of single core 12 swg copper wire (5), is wound ontothe outer surface of the former (2), and covered with an outer shell(&6), fitting within the flange (3). In the example illustrated, theouter shell (6) is in two parts and is secured to the former (2). Thetwo parts of the shell are secured together along seams (8). It isprefered that once the coil (5) has been wound onto the inner former, amixture of fibre-glass resin and catalyst are layered with fibre-glassmatting onto the coil.

A connection box (7) is provided on the shell (6) for the supply ofcurrent to the coil (5).

As is shown in more detail in FIG. 2, some or all of the ribs (4), maybe provided with a coloured layer (9) at or near to the base of eachrib. In the example given the bonding layer employed to secure the ribsto the inner surface of the former includes a coloured additive, moreparticularly carbon black mixed with the resin component of thefibre-glass. When the ribs are sufficiently worn this layer is exposedgiving a visual indication that the ribs (4) need refitting.

It should be understood that the heater can be employed withnon-conducting articles provided that a conducting body is brought intocontact with the article within the inductive heating field of the coil,such that this body is heated by eddy currents generated by the magneticflux linkage with the coil.

It is envisaged that the drum heater may be powered directly from the50Hz mains (240 volts AC), or from a suitable transformer. As it isenvisaged that the apparatus will be in the majority of embodiments aclass II appliance, it does not generally require a ground.

Various modifications may be made within the scope of the presentinvention, such as the inclusion into the drum heater of thermostaticcontrol means and/or means to give either a visible or audibleindication that the heater is in operation to prevent the exposure ofsensitive apparatus to the alternating magnetic fields produced by thecoil.

I claim:
 1. An induction heater assembly adapted for heating asubstantially cylindrical metal drum, comprising a substantiallycylindrical, substantially thermally and electrically non- conductivenon-metallic double-walled jacket having a central axis and including aninner and an outer member each member having an internal surface and anexternal surface said external surface of said inner member and saidinternal surface of said outer member defining an annular substantiallycylindrical coaxial space therebetween, an induction coil coaxiallyarranged within the substantially cylindrical space between the internaland external surfaces of said outer and inner members, respectively,water-proof non-conductive means embedding the induction coil withinsaid substantially cylindrical space, said internal surface of saidinner member being configured to receive a metal drum to be heated, aplurality of spaced, axially-extending, inwardly-directed ribs areprovided on said internal surface of said inner member for maintainingthe metal drum to be heated spaced apart from said internal surface ofsaid inner member to avoid abrasion of the latter by said internal metaldrum, each of said plurality of ribs being provided with an embeddedlayer which becomes visible when the rib is sufficiently worn down toexpose the said layer, and said jacket being constructed of materialssuch that, when the induction coil is energized with AC current while ametal drum is positioned within the jacket, the major heat transfer isto the metal drum by inducion causing it to be raised to an elevatedtemperature.
 2. An induction heater assembly as recited in claim 1wherein the embedded layer comprises carbon black, and means areprovided to mount the plurality of ribs on the jacket internal surface.